GEAR NOMENCLATURE
GEAR NOMENCLATURE
Pitch circle is a theoretical circle upon which all calculations are
based. Pitch circles of mating gears are tangent to each other.
Pinion is the smaller of two mating gears. Gear is the larger.
Circular pitch is equal to the sum of the tooth thickness and the width
of space measured on the pitch circle.
Diametral pitch is the ratio of the number of teeth to the pitch diameter.
Module is the ratio of the pitch diameter to the number of teeth (SI).
Addendum is the radial distance from the top land to the pitch circle.
GEAR NOMENCLATURE
Dedendum is the radial distance from the bottom land to the pitch
circle.
Whole depth is the sum of the addendum and dedendum.
Clearance circle is a circle that is tangent to the addendum circle of the
mating gear.
Clearance is the amount by which the dedendum in a given gear exceeds
the addendum of its mating gear.
Backlash is the amount by which the width of a tooth space exceeds the
thickness of the engaging tooth measured on the pitch circles.
INVOLUTE CURVE
RACK AND PINION
Converts rotational motion to translational motion
INTERFERENCE
A minimum number of teeth are required on the
pinion to avoid interference.
HELICAL GEARS
•Initial contact is a point
•Changes into a line as teeth
come into engagement
INVOLUTE HELICOID
WORM GEAR
Note the axis of the shafts
STRAIGHT BEVEL GEAR
SPIRAL BEVEL GEAR
HYPOID GEARS
BEVEL, HYPOID, SPIROID, WORM
Problem
A simple speed reducer is composed of 2 spur gears. The pinion gear has a
pitch diameter of 0.75” and 36 teeth while the driven gear has a pitch
diameter of 4.0” and 192 teeth.
1. What is the Diametral pitch of each gear?
2. If an electric motor rotating CCW at 3000 rpm is coupled to the pinion, what
is the rotational speed of the driven gear?
3. If the torque delivered to the pinion is 1 N-m, what is the torque on the
driven gear?
4. What is the power transmitted by the gear train?